Entinostat, which has been shown in preclinical models to enhance suppressor cells in the tumor microenvironment, was evaluated in ENCORE 601 as a treatment for non–small cell lung cancer (NSCLC), melanoma, and colorectal cancer. Previously reported phase 1 results showed that an oral dose of 5 mg weekly plus 200 mg of pembrolizumab given intravenously every 3 weeks deserved further exploration for these indications, according to Leena Gandhi, MD, who reported phase 2, stage 1 results from the lung cancer arm of the Simon two-stage study at the annual meeting of the Society for Immunotherapy of Cancer.

Treatment at that dose was studied in both anti-PD-L1–naive patients with advanced NSCLC, and in NSCLC patients who progressed on anti-PD-L1 treatment, said Dr. Gandhi of New York University Langone Medical Center.

The primary objective of stage 1 was objective response rate, and criteria for advancement were 4 or more responses out of 17 evaluable anti-PD-L1–naive patients (cohort 1), and at least 3 responses out of 31 patients who progressed on anti-PD-L1 therapy (cohort 2).

In cohort 1, two responses were confirmed and two were unconfirmed. One of the unconfirmed patients had malignant pericardial effusion, but remains on study with continued clinical benefit, Dr. Gandhi said, noting that three patients remain on study in all.

“The other notable thing I’d like to point out here … is that the majority of these were patients who did not have high levels of expression of PD-L1,” she said.

In cohort 2 patients, two responses were confirmed and one was unconfirmed. Three patients remain on study.

“In both of these cohorts there are a couple of patients who’ve had quite durable responses,” she said.

The best response to prior anti-PD-1therapy in the cohort 2 patients who had a response was stable disease (two patients). The response to prior therapy was unknown in one patient, she noted.

“All of them had clear regressions, after that initial PD-1 therapy, with this combination,” she said, noting that two had “essentially negative PD-L1 expression, and none had high levels of expression.”

Treatment was associated with grade 3/4 adverse events deemed drug related in 31% of patients; the most common of these events, occurring in at least 10% of patients in cohort 1, were hypophosphatemia and neutropenia, and in cohort 2 were fatigue, anemia, anorexia, and pneumonitis; 13% of patients discontinued treatment due to an adverse event, Dr. Gandhi said.

Of note, there were reductions in circulating myeloid derived suppressor cells in both cohorts following treatment.

Based on the responses seen in this first stage of the study, cohort 2 has advanced to stage 2 and has completed enrollment. Additional patients have not been enrolled in cohort 1, but that is still under consideration, she said.